• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Unbalanced valve/tube pre amp into monos that say need balanced inputs

No, you can't use simple RCA style cabling between the preamp you currently own and the new monoblocks that have balanced I/Ps.

The Lundahl device Walter pointed at requires an adapter that connects a 3.5 mm. miniature stereo phone plug to twin RCA plugs.

Even with the correct cabling, you might not be clear of trouble. What sort of O/P impedance does the preamp you currently employ exhibit? You can bank on the Lundahl device containing transformers. Those transformers should be driven by a low impedance source. Tell us about your current preamp.

Obviously, this is a DIY oriented "board". If you have DIY skills, you can construct what you need. A pair of something like Sowter's Model 3603 would be central to what's constructed. Again, a low driving impedance is in order.
 
210ref,
Are you using an ARC REF210 as your handle suggests?
If you are DIY capable or know someone who is, make up a cable as such: RCA centre pin to XLR male pin 2. RCA outer shell to XLR pins 1 and 3. Works in a pinch and my Ref110 doesn't seem to suffer much sonically.
Ultimately, you'll like want a balanced pre as well. On the rare occasion that I want to use my Ref3 to drive a non-balanced input amp (the SQ of Ref3 suffers noticeably driving through its RCA outputs) I have a pair of Souter 3675 trannies. The Ref3 seems quite happy driving these as long as the input impedance of the power amp is 25K ohms or higher.

Steve
 

H713

Member
2017-11-24 11:21 pm
Madison WI
The first preamp I built was a single-ended output, so I had to make an RCA to XLR cable in order to use it with my MC650 which has a balanced input.

Pin 2 goes to the center conductor on the RCA connector, pins 1 and 3 are tied to the shield of the RCA connector.

To do things properly, I'd suggest getting some Jensen transformers. Jensen sells boxes that do exactly what you need, but you can save a fair bit by building it yourself. This can also be accomplished with some op-amps. If designed well, this will be lower distortion than the xformers and will have nearly zero impact on the sound.

Building a balanced preamp with excellent performance isn't too difficult, so that may be something you want to look into.
 

kodabmx

Member
Paid Member
2011-10-31 1:00 am
Toronto
Can you not just connect it as follows? This is how I drive my Yorkville amp from my tube preamp...

EDIT: I see Steve and H713 wrote out this picture...
rca-xlr.png
 
No, you can't use simple RCA style cabling between the preamp you currently own and the new monoblocks that have balanced I/Ps.

The Lundahl device Walter pointed at requires an adapter that connects a 3.5 mm. miniature stereo phone plug to twin RCA plugs.

Even with the correct cabling, you might not be clear of trouble. What sort of O/P impedance does the preamp you currently employ exhibit? You can bank on the Lundahl device containing transformers. Those transformers should be driven by a low impedance source. Tell us about your current preamp.

Obviously, this is a DIY oriented "board". If you have DIY skills, you can construct what you need. A pair of something like Sowter's Model 3603 would be central to what's constructed. Again, a low driving impedance is in order.

Hi Eli, Primaluma Prologue
 
210ref,
Are you using an ARC REF210 as your handle suggests?
If you are DIY capable or know someone who is, make up a cable as such: RCA centre pin to XLR male pin 2. RCA outer shell to XLR pins 1 and 3. Works in a pinch and my Ref110 doesn't seem to suffer much sonically.
Ultimately, you'll like want a balanced pre as well. On the rare occasion that I want to use my Ref3 to drive a non-balanced input amp (the SQ of Ref3 suffers noticeably driving through its RCA outputs) I have a pair of Souter 3675 trannies. The Ref3 seems quite happy driving these as long as the input impedance of the power amp is 25K ohms or higher.

Steve

Thanks Steve, the Sonos converters I am borrowing might achieve this? I am going try the Selby box first as it gets here tomorrow. Yes ARC 210 ref monos, back in the day AR used to sell convertor boxes!
 
210,
If memory serves, the PL Prologue will have a fairly high O/P impedance, especially at low freq. It might not drive transformers acceptably. Try some adapters/adapter cables. In the end you'll want a REF line stage to get the most from your system. I got my REF 3 about 10 years ago. When the REF 5 came out a few people traded their 3s in on 5s. The local, well 60 miles away, dealer had two REF 3s for sale. At less than 50 cents on the dollar compared to new it was a no brainer choice. My REF 3 and REF 110 will se me out. DIY is just for fun.

Cheers, Steve